Asphalt plants typically include a rotating aggregate drier in which aggregate materials are heated and dried before being mixed with asphalt cement, an asphalt cement supply system, and a mixing tower or chamber where the aggregate materials and asphalt cement are mixed together. The drier of this arrangement is typically oriented so as to have an upper end and a lower end, so that aggregate that is introduced into the drier at the upper end will move towards the lower end by gravity flow and by the action of a series of flights mounted on the interior surface of the rotating drier. A burner is located at the lower end of the drier, and the hot air and exhaust gases from the burner move toward the upper end of the drier, against the flow of the aggregate materials. As the aggregate materials are tumbled through the exhaust gases, the materials are heated and dried. The hot, dry aggregate materials are discharged from the drier at the lower end and introduced to a mixing tower or chamber where these materials are combined with asphalt cement. As the aggregate materials are tumbled and dried in the drier, a quantity of dust is typically created and carried upwardly by the hot gases of combustion. Because of particulate emission regulations, it is unacceptable to exhaust the dust to the atmosphere. Furthermore, depending on the speed of rotation and the temperature at which the drier is operated, the quantity of dust may represent a significant portion of the fine aggregate material needed in the particular asphalt mix. Therefore, dust collection or recovery systems are known for removal of the dust from the gas stream before further processing of the combustion gases and/or exhaustion to the atmosphere. The dust which is collected in the dust recovery system may then be introduced to the mixing tower or chamber for inclusion in the asphalt mix.
It is known to provide a dust recovery system which includes an inertially driven primary collector such as a cyclone and a filter-based secondary collector such as a baghouse. In such a system, the primary collector will operate to remove the larger sized particles (i.e. larger than about 150 microns) and the secondary collector will remove the remaining particles. It is also known to provide a portable baghouse for use in connection with an asphalt plant. However, for maximum efficiency, a baghouse should be combined with an inertially driven primary collector such as a cyclone. Nevertheless, adding a cyclone to a portable baghouse assembly requires the addition of a fairly large component to a system where space is at a premium. It also requires the addition of ductwork between the primary collector and the baghouse and some provision for connecting the primary collector to a drier.
It would be desirable, therefore, if a simpler primary collector could be combined with a baghouse. It would also be desirable if such primary collector could incorporate or include a conduit for connection to a drier. Furthermore, it would be desirable if such a primary collector were capable of being stored in the enclosure of the baghouse.